A solution may contain Ag, Pb and Hg. A white precipitate forms on addition of
6 M HCl. The precipitate is insoluble in hot water. The residue turns black on
addition of ammonia. Which of the ions are present, which are absent, and which
remain undetermined? State your reasoning. Note: On paper unknowns such as this
one, conﬁrmatory tests are usually not included.
PbCl2 is soluble in hot water so it is absent
Hg2Cl2(s) + 2NH3(aq) --> Hg(s) + HgNH2Cl(s) + NH4Cl (aq) (Hg is black precipitate) AgCl is undetermined